1. Field of the Invention
The invention relates to a borosilicate retention aid composition and, a method of using the borosilicate retention aid composition in the production of paper. A method of making such borosilicate retention aid composition is also disclosed. The borosilicate materials are preferably an aqueous suspension of colloidal borosilicate.
2. Background of the Invention
In the manufacture of paper, an aqueous cellulosic suspension or furnish is formed into a paper sheet. The slurry of cellulosic fiber is generally diluted to a consistency (percent dry weight of solids in the furnish) having a fiber content of about 4 weight percent of fiber or less, and generally around 1.5% or less and often below 1.0% ahead of the paper machine, while the finished sheet typically has less than 6 weight percent water. Hence the dewatering and retention aspects of papermaking are extremely important to the efficiency and cost of the manufacture.
Gravity dewatering is the preferred method of drainage because of its relatively low cost. After gravity drainage more expensive methods are used for dewatering, for instance vacuum, pressing, felt blanket blotting and pressing, evaporation and the like. In actual practice a combination of such methods is employed to dewater, or dry, the sheet to the desired water content. Since gravity drainage is both the first dewatering method employed and the least expensive, an improvement in the efficiency of this drainage process will decrease the amount of water required to be removed by other methods and hence improve the overall efficiency of dewatering and reduce the cost thereof.
Another aspect of papermaking that is extremely important to the efficiency and cost is retention of furnish components on and within the fiber mat. The papermaking furnish represents a system containing significant amounts of small particles stabilized by colloidal forces. A papermaking furnish generally contains, in addition to cellulosic fibers, particles ranging in size from about 5 to about 1000 nm consisting of for example cellulosic fines, mineral fillers (employed to increase opacity, brightness and other paper characteristics) and other small particles that generally, without the inclusion of one or more retention aids, would in significant portion pass through the spaces (pores) between the mat formed by the cellulosic fibers on the papermachine.
Greater retention of fines, fillers, and other components of the furnish permits, for a given grade of paper, a reduction in the cellulosic fiber content of such paper. As pulps of lower quality are employed to reduce papermaking costs, the retention aspect of papermaking becomes more important because the fines content of such lower quality pulps is generally greater. Greater retention also decreases the amount of such substances lost to the whitewater and hence reduces the amount of material wastes, the cost of waste disposal and the adverse environmental effects therefrom. It is generally desirable to reduce the amount of material employed in a papermaking process for a given purpose, without diminishing the result sought. Such add-on reductions may realize both a material cost savings and handling and processing benefits.
Another important characteristic of a given papermaking process is the formation of the paper sheet produced. Formation may be determined by the variance in light transmission within a paper sheet, and a high variance is indicative of poor formation. As retention increases to a high level, for instance a retention level of 80 or 90%, the formation parameter generally declines.
Various chemical additives have been utilized in an attempt to increase the rate at which water drains from the formed sheet, and to increase the amount of fines and filler retained on the sheet. The use of high molecular weight water soluble polymers was a significant improvement in the manufacture of paper. These high molecular weight polymers act as flocculants, forming large flocs which deposit on the sheet. They also aid in the dewatering of the sheet. In order to be effective, conventional single and dual polymer retention and drainage programs require incorporation of a higher molecular weight component as part of the program. In these conventional programs, the high molecular weight component is added after a high shear point in the stock flow system leading up to the headbox of the paper machine. This is necessary since flocs are formed primarily by the bridging mechanism and their breakdown is largely irreversible and do not re-form to any significant extent. For this reason, most of the retention and drainage performance of a flocculant is lost by feeding it before a high shear point. To their detriment, feeding high molecular weight polymers after the high shear point often leads to formation problems. The feed requirements of the high molecular weight polymers and copolymers which provide improved retention often lead to a compromise between retention and formation.
While successful, high molecular weight flocculant programs were improved by the addition of so called inorganic xe2x80x9cmicroparticlesxe2x80x9d.
Polymer/microparticle programs have gained commercial success replacing the use of polymer-only retention and drainage programs in many mills. Microparticle containing programs are defined not only by the use of a microparticle component but also often by the addition points of chemicals in relation to shear. In most microparticle containing retention programs, high molecular weight polymers are added either before or after at least one high shear point. The inorganic microparticulate material is then usually added to the furnish after the stock has been flocculated with the high molecular weight component and sheared to break down those flocs. The microparticle addition re-flocculates the furnish, resulting in retention and drainage that is at least as good as that attained using the high molecular weight component in the conventional way (after shear), with no deleterious impact on formation.
One such program employed to provide an improved combination of retention and dewatering is described in U.S. Pat. Nos. 4,753,710 and 4,913,775, to Langley et al., the disclosures of which are hereinafter incorporated by reference into this specification. In the method disclosed in Langley et al., a high molecular weight linear cationic polymer is added to the aqueous cellulosic papermaking suspension before shear is applied to the suspension, followed by the addition of bentonite after the shear application. Shearing is generally provided by one or more of the cleaning, mixing and pumping stages of the papermaking process, and the shear breaks down the large flocs formed by the high molecular weight polymer into microflocs. Further agglomeration then ensues with the addition of the bentonite clay particles.
Other such microparticle programs are based on the use of colloidal silica as a microparticle in combination with cationic starch such as that described in U.S. Pat. Nos. 4,388,150 and 4,385,961, the disclosures of which are hereinafter incorporated by reference into this specification, or the use of a cationic starch, flocculant, and silica sol combination such as that described in both U.S. Pat. Nos. 5,098,520 and 5,185,062, the disclosures of which are also hereinafter incorporated by reference into this specification. U.S. Pat. No. 4,643,801 claims a method for the preparation of paper using a high molecular weight anionic water soluble polymer, a dispersed silica, and a cationic starch.
Although, as described above, the microparticle is typically added to the furnish after the flocculant and after at least one shear zone, the microparticle effect can also be observed if the microparticle is added before the flocculant and the shear zone (e.g., wherein the microparticle is added before the screen and the flocculant after the shear zone).
In a single polymer/microparticle retention and drainage aid program, a flocculant, typically a cationic polymer, is the only polymer material added along with the microparticle. Another method of improving the flocculation of cellulosic fines, mineral fillers and other furnish components on the fiber mat using a microparticle is in combination with a dual polymer program which uses, in addition to the microparticle, a coagulant and flocculant system. In such a system a coagulant is first added, for instance a low molecular weight synthetic cationic polymer or cationic starch. The coagulant may also be an inorganic coagulant such as alum or polyaluminum chlorides. This addition can take place at one or several points within the furnish make up system, including but not limited to the thick stock, white water system, or thin stock of a machine. This coagulant generally reduces the negative surface charges present on the particles in the furnish, particularly cellulosic fines and mineral fillers, and thereby accomplishes a degree of agglomeration of such particles. The coagulant treatment is followed by the addition of a flocculant. Such a flocculaqnt generally is a high molecular weight synthetic polymer which bridges the particles and/or agglomerates, from one surface to another, binding the particles into larger agglomerates. The presence of such large agglomerates in the furnish, as the fiber mat of the paper sheet is being formed, increases retention. The agglomerates are filtered out of the water onto the fiber web, whereas unagglomerated particles would, to a great extent, pass through such a paper web. In such a program the order of addition of the microparticle and flocculant can be reversed successfully.
The present invention departs from the disclosures of these patents in that a borosilicate, preferably a colloidal borosilicate is utilized as the microparticle. Surprisingly we have found that borosilicates provide improved performance over other microparticle programs, and especially those using colloidal silica sols as the microparticle. The borosilicate microparticles of the invention allow the production of paper and board having improved levels of retention, formation, uniform porosity, and overall dewatering.
One aspect of the invention comprises a borosilicate retention aid composition. The borosilicates, preferably aqueous solutions of colloidal particles of borosilicate, useful in this invention have a mole ratio of boron to silicon of from 1:1000 to 100:1 and generally from 1:100 to 2:5. Preferably the mole ratio of sodium to silicon in the borosilicate materials of this invention ranges from 0.006 to 1.04 and even more preferably ranges between 0.01 to 0.7. A further aspect of the invention comprises a papermaking system which comprises the steps of adding to a papermaking furnish from about 0.00005 to about 1.25% by weight, based on the weight of the dry fiber in the furnish, of a borosilicate. In an alternative embodiment, a nonionic, cationic, or anionic polymeric flocculant is added to the furnish either before or after addition of the borosilicate in an amount of from about 0.001 to about 0.50% by weight based on the dry weight of fiber in the furnish. An alternative is the addition of cationic starch or guar gum in place of or in addition to a polymeric flocculant to the furnish either before or after addition of the borosilicate in an amount of from about 0.005 to about 5.0% by weight based on the dry weight of fiber in the furnish. Another alternative is the addition of a coagulant to the furnish in an amount ranging from 0.005 to 1.25% by weight of the dry weight of the fiber in the furnish. The flocculation of components of the papermaking furnish is increased when the borosilicate is added alone or in combination with a conventional polymeric flocculant, alone or in combination with a coagulant.
By the addition of the borosilicate particles of this invention to a papermaking furnish or slurry prior to sheet formation, improved sheet properties may be obtained. As used herein, the term furnish or slurry is meant as a suspension of cellulosic fibers used to form a cellulosic sheet. The sheet may be a fine paper (which as used herein includes virgin-fiber-based as well as recycle-fiber based materials), board (which as used herein includes recycle-fiber based test liner and corrugating medium as well as virgin-fiber based materials),and newsprint (which as used herein includes magazine furnishes as well as both virgin fiber and recycle-fiber based), or other cellulosic material. The final sheet may contain in addition to a cellulosic fiber mat, fillers, pigments, brighteners, sizing agents, and other materials used in the production of the numerous grades of cellulosic mats commonly referred to as paper or board.
The invention comprises a retention and drainage aid composition comprising a borosilicate (preferably a colloidal borosilicate) having a mole ratio of boron to silicon ranging from about 1:100 to about 2:5. In a preferred embodiment of the invention, the borosilicate is characterized as having a mole ratio of sodium to silicon ranging from about 6:1000 to 1.04:1. The microparticle retention aid is preferably a colloid of borosilicate having a chemistry similar to that of borosilicate glass. The borosilicate is preferably used in the form of an aqueous colloid. This colloid is generally prepared by reacting an alkali metal salt of a boron containing compound with silicic acid under conditions resulting in the formation of a colloid. The borosilicate particles useful in this invention may have a particle size over a wide range, for example from 1 nm (nanometer) to 2 microns (2000 nm), and preferably from 1 nm to 1 micron. When a colloidal borosilicate is utilized the particle size will generally be in the range of from 1 nm to 200 nm and preferably from 1 to 80 nm and most preferably 20-80 nm. The surface area of the borosilicate particles useful in this invention can likewise vary over a wide range. Generally as particle size decreases, surface area will increase. The surface area should be in the range of 15 to 3000 m2/g and preferably 50 to 3000 m2/g. When the preferred colloidal borosilicate particles of the invention are utilized the surface area will generally be in the range of 250 to 3000 m2/g and preferably from 700 to 3000 m2/g.
The preferred colloidal borosilicate materials useful in this invention are generally prepared by first preparing silicic acid. This may be advantageously accomplished by contacting an alkali metal silicate solution, preferably a dilute solution of the alkali metal silicate with a commercial cation exchange resin, preferably a so called strong acid resin, in the hydrogen form and recovering a dilute solution of silicic acid. The silicic acid may then be added, with agitation to a dilute solution of an alkali metal borate at a pH of from 6-14, and a colloidal borosilicate product suspended in water is recovered. Alternatively, the alkali metal borate and the silicic acid may be added simultaneously to prepare suitable materials. In the usual practice of this invention, the concentration of the silicic acid solution utilized is generally from 3 to 8 percent by weight SiO2, and preferably 5 to 7 percent by weight SiO2. The weight percent of the borate solution utilized is generally 0.01 to 30 and preferably 0.4 to 20 weight percent as B2O3. The borate salt utilized may range over a wide variety of compounds. Commercial borax, sodium tetraborate decahydrate, or sodium tetraborate pentahydrate are the preferred material in the practice of this invention because of the ready availability of these materials and their low cost. Other water soluble borate materials may be utilized. We believe that any soluble alkali metal borate salt may be employed in the practice of this invention. The preparation of the colloidal borosilicate material of this invention may be accomplished with or without pH adjustment. It is sometimes advisable to conduct the reaction at a pH of 7.5 to 10.5 through the addition of an appropriate alkali metal hydroxide, preferably sodium hydroxide, to the reaction mixture. Best results have been obtained in the pH range of 8 to 9.5 although as will be appreciated, the synthesis procedures for the borosilicate compositions of this invention are still being optimized. We believe that agitation, rate of addition, and other parameters are non-critical to the formation of the colloidal borosilicate compositions of the invention. Other methods of preparing the colloidal borosilicates of this invention may also be utilized. These methods could encompass preparing the colloidal borosilicate as above and spray drying the particles followed by grinding, or other methods which would yield a borosilicate material meeting the parameters set forth above.
The invention further comprises a method of improving the production of paper which comprises the step of adding to a paper mill furnish from about 0.00005 to about 1.25% by weight based on the dry weight of fiber in the slurry or furnish of a borosilicate, preferably a colloidal borosilicate. In an alternative embodiment, a nonionic, cationic or anionic polymeric flocculant may be added to the furnish either before or after the addition of the borosilicate in an amount of from about 0.001 to about 0.5% by weight based on dry weight of fiber in the furnish. A cationic starch may alternatively be added to the furnish in place of, or in addition to the synthetic polymer flocculant in an amount of from about 0.005 to about 5.0% by weight based on the dry weight of fiber in the furnish. More preferably, the starch is added in an amount of from about 0.05 to about 1.5% by weight based on the dry weight of fiber in the furnish. In yet another embodiment, a coagulant may be added to the furnish in place of, or in addition to, the flocculent and/or the starch in an amount of from about 0.005 to about 1.25% by weight based on the dry weight of fiber in the papermaking furnish. Preferably the coagulant is added in an amount of from about 0.025 to about 0.5% by weight based on the dry weight of fiber in the furnish.
This invention is also directed to a method for increasing retention and drainage of a papermaking furnish on a papermaking machine which comprises the steps of adding to a papermaking furnish from about 0.00005 to about 1.25% by weight based on the dry weight of fiber in the furnish of a borosilicate particle, preferably a colloidal borosilicate. The borosilicate may be added to the papermaking furnish along with a nonionic, cationic or anionic polymeric flocculant. The flocculant may be added either before or after the borosilicate in an amount of from about 0.001 to about 0.5% by weight based on the dry weight of fiber in the furnish. Starch may alternatively be added to the furnish in place of or in addition to the flocculant in an amount of from about 0.005 to about 5.0% by weight based on dry weight of fiber in the furnish. If starch is utilized it is preferably a cationic starch. When used, the starch is preferably added in an amount of from about 0.05 to about 1.5% by weight based on the dry weight of fiber in the furnish. In yet another alternative, a coagulant may be added to the furnish in place of, or in addition to, the flocculant and/or the starch in an amount of from about 0.005 to about 1.25% by weight based on the dry weight of fiber in the furnish. Preferably, the coagulant is added in an amount of from about 0.025 to about 0.5% by weight based on the dry weight of fiber in the furnish.
The dosage of the polymeric flocculant in any of the above embodiments is preferably from 0.005 to about 0.2 weight percent based on the dry weight of fiber in the furnish. The dosage of the borosilicate is preferably from about 0.005 to about 0.25 percent by weight based on the weight of dry fiber in the furnish, and most preferably from about 0.005 to about 0.15% by weight of fiber in the furnish.
It should be pointed out that since this invention is applicable to a broad range of paper grades and furnishes the percentages given above may occasionally vary. It is within the spirit and intent of the invention that variance can be made from the percentages given above without departing from the invention, and these percentage values are given only as guidance to one skilled in the art.
In any of the above embodiments, bentonite, talc, synthetic clays, hectorite, kaolin, or mixtures thereof may also be added anywhere in the papermaking system prior to sheet formation. The preferred addition point is the thick stock pulp before dilution with whitewater. This application results in increased cleanliness of the papermaking operation which otherwise experiences hydrophobic deposition affecting both the productivity and the quality of paper.
In addition, any of the above embodiments may be applied to papermaking furnish selected from the group consisting of fine paper, (which as used herein includes virgin fiber based as well as recycle-fiber based materials), board (which as used herein includes recycle-fiber based test liner and corrugating medium as well as virgin-fiber based materials), and newsprint (which as used herein includes magazine furnishes as well as both virgin fiber and recycle-fiber based), or other cellulosic material. These furnishes include those that are wood-containing, wood-free, virgin, bleached recycled, unbleached recycled, and mixtures thereof.
Paper or paperboard is generally made from a suspension or furnish of cellulosic material in an aqueous medium, which furnish is subjected to one or more shear stages, in which such stages generally are a cleaning stage, a mixing stage and a pumping stage, and thereafter the suspension is drained to form a sheet, which sheet is then dried to the desired, and generally low, water concentration. The borosilicate materials of the invention may be added to the furnish before or after a shear stage.
In addition to the retention and drainage aid applications described above, the borosilicate materials may be used in conjunction with standard cationic wet strength resins to improve the wet strength of cellulosic sheet so treated. When utilized in this manner the borosilicate is added to the furnish prior to placement of the furnish, containing the wet strength resin, on a papermachine. The borosilicate is generally utilized at the levels set forth above.
The borosilicate of this invention has been found to significantly enhance the performance of synthetic polymeric flocculants and retention aids, and starch in the papermaking process. Further, the borosilicate materials are believed to have utility as additives in solids/liquids separation processes such as water pretreatment, and in wastewater treatment applications. The borosilicates in addition to enhancing drainage and retention in newsprint, fine paper, board and other paper grades, may also find utility in pitch and stickies control in papermaking, pulp dewatering in the production of dry-lap pulp, saveall and clarifier applications in pulp and paper mills, water clarification dissolved air flotation and sludge dewatering. The compositions of this invention may also find utility in solid/liquid separation or emulsion breaking. Examples of such applications are municipal sludge dewatering, the clarification and dewatering of aqueous mineral slurries, refinery emulsion breaking and the like. The enhanced performance seen utilizing the borosilicate particles of this invention in combination with synthetic polymers and or starch includes higher retention, improved drainage and improved solids/liquids separation, and often a reduction in the amount of polymer or starch used to achieve the desired effect.
Microparticle retention programs are based on the restoration of the originally formed flocs broken by shear. In such applications, the flocculant is added before at least one high shear point, followed by the addition of microparticle just before the headbox. Typically, a flocculant will be added before the pressure screens, followed by the addition of microparticle after the screens. However a method wherein this order may be reversed is contemplated herein. Secondary flocs formed by the addition of microparticles result in increased retention and drainage without detrimentally affecting formation of the sheet. This allows increased filler content in the sheet, eliminates two-sidedness of the sheet, and increases drainage and speed of the machine in paper manufacturing.
The use of a slight excess of polymeric flocculant and/or coagulant is believed necessary to ensure that the subsequent shearing results in the formation of microflocs which contain or carry sufficient polymer to render at least parts of their surfaces positively charged, although it is not necessary to render the whole furnish positively charged. Thus the zeta potential of the furnish, after the addition of the polymer and after the shear stage, may be cationic or anionic.
Shear may be provided by a device in the apparatus used for other purposes, such as a mixing pump, fan pump or centriscreen or one may insert into the apparatus a shear mixer or other shear stage for the purpose of providing shear, and preferably a high degree of shear, subsequent to the addition of the polymer.
The flocculants used in the application of this invention are high molecular weight water soluble or dispersible polymers which may have a cationic or anionic charge. Nonionic high molecular weight polymers may also be utilized. These polymers may be completely soluble in the papermaking system, or alternatively may be readily dispersible. They may have a branched or crosslinked structure provided that they do not form objectionable xe2x80x9cfish eyesxe2x80x9d, so called globs of undissolved polymer on the finished paper. Polymers of these types are readily available from a variety of commercial sources. They are available as dry solids, aqueous solutions, water-in-oil emulsions which when added to water allow the polymer contained therein to rapidly solubilize, or as dispersions of the water soluble or dispersible polymer in aqueous brine solutions. The form of the high molecular weight flocculant used herein is not deemed to be critical so long as the polymer is soluble or dispersible in the furnish.
As stated above, the polymers may be cationic, anionic, or nonionic. Cationic polymer flocculants useful herein are generally high molecular vinyl addition polymers which incorporate a cationic functional group. These polymers are generally homopolymers of water soluble cationic vinyl monomers, or may be copolymers of a water soluble cationic vinyl monomer with a nonionic monomer such as acrylamide or methacrylamide. The polymers may contain only one cationic vinyl monomer, or may contain more than one cationic vinyl monomer. Alternatively, certain polymers may be modified or derivatized after polymerization such as polyacrylamide by the mannich reaction to produce a cationic vinyl polymer useful in the invention. The polymers may have been prepared from as little as 1 mole percent cationic monomer to 100 mole percent cationic monomer, or from a cationically modified functional group on a post polymerization modified polymer. Most often the cationic flocculants will have at least 5 mole percent of cationic vinyl monomer or functional group, and most preferably, at least 10 weight percent of cationic vinyl monomer or functional group.
Suitable cationic vinyl monomers useful in making the cationically charged vinyl addition copolymers and homopolymers of this invention will be well known to those skilled in the art. These materials include: dimethylaminoethyl methacrylate (DMAEM), dimethylaminoethyl acrylate (DMAEA), diethylaminoethyl acrylate (DEAEA), diethylaminoethyl methacrylate (DEAEM) or their quaternary ammonium forms made with dimethyl sulfate or methyl chloride, mannich reaction modified polyacrylamides, diallylcyclohexylamine hydrochloride (DACHA HCl), diallyldimethylammonium chloride (DADMAC), methacrylamidopropyltrimethylammonium chloride (MAPTAC) and allyl amine (ALA). Cationized starch may also be used as a flocculant herein. The flocculant selected may be a mixture of those stated above, or a mixture of those stated above with a cationic starch. Those skilled in the art of cationic polymer based retention programs will readily appreciate that the selection of a particular polymer is furnish, filler, grade, and water quality dependent.
High molecular weight anionic flocculants which may be useful in this invention are preferably water-soluble or dispersible vinyl polymers containing 1 mole percent or more of a monomer having an anionic charge. Accordingly, these polymers may be homopolymers or water soluble anionically charged vinyl monomers, or copolymers of these monomers with for instance non-ionic monomers such as acrylamide or methacrylamide. Examples of suitable anionic monomers include acrylic acid, methacrylamide 2-acrylamido-2-methylpropane sulfonate (AMPS) and mixture thereof as well as their corresponding water soluble or dispersible alkali metal and ammonium salts. The anionic high molecular weight polymers useful in this invention may also be either hydrolyzed acrylamide polymers or copolymers of acrylamide or its homologues, such as methacrylamide, with acrylic acid or its homologues, such as methacrylic acid, or with polymers of such vinyl monomers as maleic acid, itaconic acid, vinyl sulfonic acid, or other sulfonate containing monomers. Anionic polymers may contain sulfonate or phosphonate functional groups or mixtures thereof, and may be prepared by derivatizing polyacrylamide or polymethacrylamide polymers or copolymers. The most preferred high molecular weight anionic flocculants are acrylic acid/acrylamide copolymers, and sulfonate containing polymers such as those prepared by the polymerization of such monomers as 2-acrylamide-2-methylpropane sulfonate, acrylamido methane sulfonate, acrylamido ethane sulfonate and 2-hydroxy-3-acrylamide propane sulfonate with acrylamide or other non-ionic vinyl monomer. When used herein the polymers and copolymers of the anionic vinyl monomer may contain as little as 1 mole percent of the anionically charged monomer, and preferably at least 10 mole percent of the anionic monomer. Again the choice of the use of a particular anionic polymer will be dependent upon furnish, filler, water quality, paper grade, and the like.
While most microparticle programs perform well with only a high molecular weight cationic flocculant, we have seen surprising effects using the borosilicate particles of the invention with high molecular weight anionic water soluble flocculants with the addition of a cationic coagulant.
Nonionic flocculants useful in this invention may be selected from the group consisting of polyethylene oxide and poly(meth)acrylamide. In addition to the above, it may be advantageous to utilize so called amphoteric water soluble polymers in certain cases. These polymers carry both a cationic and an anionic charge in the same polymer chain.
The nonionic, cationic and anionic vinyl polymer flocculants useful herein will generally have a molecular weight of at least 500,000 daltons, and preferably molecular weights of 1,000,000 daltons and higher. Water soluble and/or dispersible flocculants useful herein may have a molecular weight of 5,000,000, or higher, for instance in the range of from 10 to 30 million or higher. The polymers of the invention may be entirely water soluble when applied to the system, or may be slightly branched (two-dimensional) or slightly cross linked (three dimensional) so long as the polymers are dispersible in water. The use of polymers which are entirely water soluble are preferred, but dispersible polymers, such as those described in WO 97/16598, may be employed. Polymers useful may be substantially linear as such term is defined in Langley et. al., U.S. Pat. No. 4,753,710. The upper limit for molecular weight is governed by the solubility or dispersiblity of the resulting product in the papermaking furnish.
Cationic or amphoteric starches useful in the application of this invention are generally described in U.S. Pat. No. 4,385,961. the disclosure of which has been incorporated by reference into this specification. Cationic starch materials are generally selected from the group consisting of naturally occurring polymers based on carbohydrates such as guar gum and starch. The cationic starch materials believed to be most useful in the practice of this invention include starch materials derived from wheat, potato and rice. These materials may in turn be reacted to substitute ammonium groups onto the starch backbone, or cationize in accordance with the process suggested by Dondeyne et al. in WO 96/30591. In general starches useful in this invention have a degree of substitution (d.s.) of ammonium groups within the starch molecule between about 0.01 and 0.05. The d.s. is obtained by reacting the base starch with either 3-chloro-2-hydroxypropyl-trimethylammonium chloride or 2,3-epoxypropyl-trimethylammonium chloride to obtain the cationized starch. As will be appreciated it is beyond the scope and intent of this invention to describe means for the cationizing of starch materials and these modified starch materials are well known and are readily available from a variety of commercial sources.
Various characteristics of the cellulosic furnish, such as pH, hardness, ionic strength and cationic demand, may affect the performance of a flocculant in a given application. The choice of flocculant involves consideration of the type of charge, charge density, molecular weight and type of monomers and is particularly dependent upon the water chemistry of the furnish being treated.
Other additives may be charged to the cellulosic furnish without any substantial interference with the activity of the present invention. Such other additives include for instance sizing agents, such as alum and rosin, pitch control agents, extenders, biocides and the like. The cellulosic furnish to which the retention aid program of the invention is added may also contain pigments and or fillers such as titanium dioxide, precipitated and/or ground calcium carbonate, or other mineral or organic fillers. It may be possible, and it is within the spirit of the invention that the instant invention may be combined with other so called microparticle programs such as bentonite, kaolin, and silica sols. However data demonstrated herein shows that the particles of the subject invention out perform these materials, and the combination thereof may yield a performance level less than either of the materials by themselves. Nevertheless, when papermakers change grades or furnishes it is possible that in certain situations the combination of the borosilicate materials of the invention with other microparticles may be practical and desirable.
The borosilicate microparticles of the invention may also be used in combination with a coagulant according to the teachings of Sofia et. al., U.S. Pat. No. 4,795,531, the disclosure of which is hereinafter incorporated by reference into this specification. Sofia teaches a microparticle program in which a microparticle is utilized in the presence of a cationic coagulant and a high molecular weight charged flocculant.
The cationic coagulant materials which may find use in this aspect of the invention include well known commercially available low-to mid molecular weight water soluble polyalkylenepolyamines including those prepared by the reaction of an alkylene polyamine with a difunctional alkyl halide. Materials of this type include condensation polymers prepared from the reaction of ethylenedichloride and ammonias, ethylene dichloride, ammonia and a secondary amine such as dimethyl amine, epichlorohydrin-dimethylamine, epichlorohydrin-dimethylamine-ammonia, polyethyleneimines, and the like. Also useful will be low molecular weight solution polymers and copolymers of vinyl monomers such as diallyldimethylammonium halides, especially diallyldimethylammonium chloride, dialkylaminoalkylacrylates, dialkylaminoalkylacrylate quaternaries, and the like where xe2x80x98alkylxe2x80x99 is meant to designate a group having 1-4, and preferably 1-2 carbon atoms. Preferably xe2x80x98alkylxe2x80x99 is methyl. These monomers are exemplified by such materials as dimethylaminoethyl acrylate, dimethyl-aminoethyl methacrylate and their water-soluble quaternary ammonium salts. In certain cases cationic starch may be employed as the coagulant. Inorganic coagulants, e.g., alum and polyaluminum chloride, may also be used in this invention. The usage rate of inorganic coagulants is typically from 0.05 to 2 weight percent based on the dry weight of fiber in the furnish. The use of a coagulant with the borosilicate microparticles of this invention is optional.
The present method is applicable to all grades and types of paper products that contain the fillers described herein, and further applicable for use on all types of pulps including, without limitation, chemical pulps, including sulfate and sulfite pulps from both hardwood and softwood, thermo-mechanical pulps, mechanical pulps and groundwood pulps.
The amount of any mineral filler used in the papermaking process, generally employed in a papermaking stock is from about 10 to about 30 parts by weight of the filler per hundred parts by weight of dry fiber in the furnish, but the amount of such filler may at times be as low as about 5, or even 0, parts by weight, and as high as about 40 or even 50 parts by weight, same basis.